When Airy beams — which travel without diffraction in a curved arc in free space — are coupled with surface plasmon polaritons (SPP), researchers have found that they can manipulate light at an extremely small scale beyond the diffraction limit.

Examples of the dynamic control of the plasmonic Airy beams show switching the trajectories to various directions (a,b) and bypassing obstacles (gray solid circle in c). Left panels are numerical simulations, right panels are experimental demonstrations. (Image: Xiang Zhang group)
By directing a laser beam across the surface of a metal nanostructure, it generates electronic surface waves (plasmons) that roll through the metal’s conduction electrons — this interaction creates the SPPs.

“Up to now, different plasmonic elements for manipulating surface plasmons were realized either through structuring metal surfaces or by placing dielectric structures on metals,” said Peng Zhang, lead author of the study from Lawrence Berkeley National Laboratory (LBNL). “Both approaches are based on the fabrication of permanent nanostructures on the metal surface, which are very difficult if not impossible to reconfigure in real time. Reconfigurability is crucial to optical interconnections, which in turn are crucial for high-performance optical computing and communication systems. The reconfigurability of our technique is a huge advantage over previous approaches.”

(L to R) Yongmin Liu, Xiang Zhang, Peng Zhang and Sheng Wang were part of a team that developed the first technique for dynamically controlling plasmonic Airy beams without the need for waveguides or other permanent structures. (Image: Roy Kaltschmidt, Berkeley Lab)
The dynamic control of the plasmonic Airy beams is provided by a computer-controlled spatial light modulator, a device similar to an LCD, which can be used to offset the incoming light waves from a laser beam with respect to a cubic phase system mask and a Fourier lens. This generates a plasmonic Airy beam on the surface of a metal whose ballistic motion can be modified.

This image shows the computer-based dynamic control of the trajectory and peak intensity position of plasmonic Airy beams. (Image: Xiang Zhang group)
“Dynamic controllability of SPPs is extremely desirable for reconfigurable optical interconnections,” said Xiang Zhang, LBNL scientist and head of the research group. “We have provided a novel approach of plasmonic Airy beam to manipulate SPPs without the need of any waveguide structures over metallic surfaces, providing dynamic control of their ballistic trajectories despite any surface roughness and defects, or even getting around obstacles. This is promising not only for applications in reconfigurable optical interconnections, but also for precisely manipulating particles on extremely small scales.”

Team members Sheng Wang, Yongmin Liu, Xiaobo Yin, Changgui Lu and Zhigang Chen were collaborators in the study, which was published in Optics Letters.